New reagents are being developed for the synthesis of substances of biological importance. From earlier work on the tetracarbonyliron complexes of alkenes, di-t-butyl methylenemalonate has emerged as a unique synthon for vinyl ketones and for the construction of the polycyclic fused-ring system found in steroids and other natural products. A specific objective of the project is to develop an efficient synthesis of estrone using this reagent. Earlier work has also led to the development of a new macrolide synthesis, namely intramolecular cyclization of terracarbonyliron complexes of acrylate esters. Current work is directed toward defining the scope of this methodology and applying it to the synthesis of naturally occurring macrolide systems.